UL4703 PV Cable AWG Calculator
Size your solar DC cable in seconds per NEC 690.8. Get the right AWG, voltage drop, and product recommendation — free, no signup required.
Project Parameters
Module Specs
Installation
Result
Enter your parameters and click Calculate to see the recommended UL4703 PV cable for your installation.
NEC 690.8 PV Wire Sizing Calculator — How It Works
This NEC 690.8 PV cable sizing calculator determines the correct AWG for your UL4703 photovoltaic cable in seconds. It implements the full conductor sizing methodology required by the 2023 National Electrical Code Article 690 for PV source and output circuits, including the 1.25 × 1.25 ampacity factors, NEC 310.15(B)(2)(a) temperature correction, NEC 310.15(B)(3)(a) bundling adjustment, NEC 240.4(D) small conductor rule enforcement, and DC voltage drop verification.
Just enter your module's short-circuit current (Isc), maximum power voltage (Vmp), modules per string, conduit ambient temperature, and one-way distance. The calculator returns the smallest AWG that simultaneously meets every NEC ampacity requirement and stays under your project's voltage drop tolerance — plus a direct link to the recommended UL4703 PV wire product in stock.
Step-by-Step: The Methodology Behind the Calculator
- Maximum circuit current — multiplies module Isc by 1.25 per NEC 690.8(A)(1) to account for solar irradiance above 1000 W/m².
- Method A required ampacity — multiplies again by 1.25 per NEC 690.8(B)(1) to determine the base 90 °C column ampacity required.
- Required OCPD — rounds up to the next standard fuse/breaker size per NEC 690.9(B) and 240.6(A).
- Temperature correction — applies NEC 310.15(B)(2)(a) factor to derate base ampacity for installation ambient.
- Bundling adjustment — applies NEC 310.15(B)(3)(a) factor when more than three current-carrying conductors share a conduit.
- Small conductor rule — enforces NEC 240.4(D): 14 AWG ≤ 15 A OCPD, 12 AWG ≤ 20 A, 10 AWG ≤ 30 A.
- Voltage drop check — calculates two-way DC loss using XLPE PV cable resistance at 75 °C and verifies it stays below your tolerance.
Reference: UL4703 PV Cable Ampacity Table (NEC 90 °C / 75 °C)
Base ampacities for tinned copper UL4703 conductors before derating. Use these values as a sanity check against the calculator output.
| AWG | Cross-section (mm²) | Ampacity 90 °C (A) | Ampacity 75 °C (A) | Resistance (Ω/1000 ft) | Typical use |
|---|---|---|---|---|---|
| 14 | 2.08 | 25 | 20 | 3.140 | Rare in PV; OCPD limited to 15 A |
| 12 | 3.31 | 30 | 25 | 1.980 | Small residential, low-Isc modules |
| 10 | 5.26 | 40 | 35 | 1.240 | ★ Most common residential / C&I |
| 8 | 8.37 | 55 | 50 | 0.778 | Long runs, bifacial modules, 13–15 A Isc |
| 6 | 13.3 | 75 | 65 | 0.491 | Combiner-to-inverter, parallel strings |
| 4 | 21.2 | 95 | 85 | 0.308 | DC feeders, commercial |
| 2 | 33.6 | 130 | 115 | 0.194 | Recombiner / inverter feeds |
| 1/0 | 53.5 | 170 | 150 | 0.122 | Utility-scale DC feeders |
| 4/0 | 107 | 260 | 230 | 0.061 | Large commercial / utility |
Source: NEC 2023 Table 310.16 for 90 °C copper conductors with XLPE/RHW-2/USE-2 insulation. Resistance values per Class 5 stranded tinned copper at 75 °C.
Reference: NEC 310.15(B)(2)(a) Temperature Correction Factors (90 °C insulation)
| Ambient (°C) | Ambient (°F) | Correction factor |
|---|---|---|
| ≤ 25 | ≤ 77 | 0.96 |
| 26–30 | 78–86 | 0.91 |
| 31–35 | 87–95 | 0.87 |
| 36–40 | 96–104 | 0.82 |
| 41–45 | 105–113 | 0.76 |
| 46–50 | 114–122 | 0.71 |
| 51–55 | 123–131 | 0.65 |
| 56–60 | 132–140 | 0.58 |
| 61–65 | 141–149 | 0.50 |
| 66–70 | 150–158 | 0.41 |
| 71–75 | 159–167 | 0.29 |
Rooftop conduit in the southern US frequently reaches 60–70 °C (140–158 °F) under full sun. Always design for the worst case.
Reference: NEC 310.15(B)(3)(a) Bundling Adjustment Factors
| Current-carrying conductors | Adjustment factor |
|---|---|
| 1–3 | 1.00 |
| 4–6 | 0.80 |
| 7–9 | 0.70 |
| 10–20 | 0.50 |
| 21–30 | 0.45 |
| 31–40 | 0.40 |
| 41+ | 0.35 |
Worked Examples
Example 1 — Typical Residential Rooftop (10 modules)
Inputs: Isc = 11 A · Vmp = 34 V · 10 modules per string · 50 ft one-way · ambient 45 °C · 4 conductors bundled · 2% VD target.
- Maximum current: 11 × 1.25 = 13.75 A
- Method A required: 13.75 × 1.25 = 17.19 A → required OCPD = 20 A
- Combined derating: 0.76 × 0.80 = 0.608
- 10 AWG derated ampacity: 40 × 0.608 = 24.3 A → capped at 75 °C column = 35 A → meets ampacity ✓
- String voltage: 34 × 10 = 340 V · Voltage drop: ~1.4% ✓
- Result: 10 AWG UL4703 · use 10 AWG 2000V 500 ft or 1000 ft reel
Example 2 — High-Isc Bifacial Modules, Long Run
Inputs: Isc = 14.5 A · Vmp = 41 V · 12 modules per string · 150 ft one-way · ambient 50 °C · 6 conductors bundled · 2% VD target.
- Maximum current: 14.5 × 1.25 = 18.13 A
- Method A required: 18.13 × 1.25 = 22.66 A → required OCPD = 25 A
- 10 AWG derated: 40 × (0.71 × 0.80) = 22.7 A → marginal · 240.4(D) limits 10 AWG to 30 A OCPD ✓
- 10 AWG voltage drop at 150 ft: ~3.2% — exceeds 2% target ✗
- Result: 8 AWG UL4703 for voltage drop compliance · use 8 AWG 2000V 500 ft
Example 3 — Utility-Scale DC Feeder
Inputs: 8 parallel strings combined into one feeder at 95 A operating · 300 ft to inverter · ambient 45 °C · single feeder · 1.5% VD target.
- Maximum current: 95 × 1.25 × 1.25 = 148.4 A → required OCPD = 150 A
- 2 AWG ampacity at 90 °C = 130 A · derated 0.76 = 98.8 A — fails Method A
- 1/0 AWG ampacity at 90 °C = 170 A · derated 0.76 = 129 A — meets ampacity ✓
- 1/0 AWG voltage drop at 300 ft: ~1.0% ✓
- Result: 1/0 AWG UL4703 — for utility solar, consider aluminum 500 MCM for cost efficiency on long feeders
UL4703 Cable Voltage & Insulation Selection
2000V vs 600V — Which Should You Specify?
For any modern grid-tied or commercial solar installation, 2000V UL4703 PV cable is the recommended choice. Most string inverters operate at 1000–1500 V DC, and 2000V cable provides safety margin, complies with utility interconnection rules, and prevents code-update issues if the system is later expanded. 600V PV wire remains valid for small residential systems and off-grid arrays where string Voc stays well below 600 V even at the coldest design temperature per NEC 690.7.
Why XLPE Insulation Matters
Cross-linked polyethylene (XLPE) is the standard insulation for UL4703 PV wire because of its exceptional resistance to UV, ozone, moisture, and abrasion — properties that determine whether your cable lasts 5 years or 25. All PhotovoltaicCable.com UL4703 wire uses Class 5 stranded tinned copper with chemically cross-linked XLPE jacketing rated for -40 °C to 90 °C wet (150 °C dry) and UL VW-1 flame test compliance.
Common Sizing Mistakes to Avoid
- Forgetting 240.4(D) — sizing 14 AWG to a 17 A circuit may pass ampacity math but fails the small conductor rule. The calculator enforces this automatically.
- Underestimating ambient — using outdoor air temperature instead of conduit-on-roof temperature can underspec by one or two AWG sizes. Use 60–70 °C for southern US rooftops.
- Counting only one circuit's conductors when multiple strings share a conduit. NEC 310.15(B)(3)(a) counts every current-carrying conductor in the bundle.
- Ignoring the 75 °C terminal cap — even if 90 °C insulation derates above 90 °C ampacity, NEC 110.14(C) caps the conductor at the terminal block's listed temperature (typically 75 °C).
- Skipping voltage drop — passing ampacity does not equal economic operation. A 3% voltage drop wastes ~3% of system production for 25 years.
About PhotovoltaicCable.com
PhotovoltaicCable.com is the #1 supplier of UL4703-certified PV wire for professional solar installers in the United States. We stock 6, 8, 10, and 12 AWG copper PV wire and 500 MCM aluminum DC feeders in 500, 1,000, 2,500, and 5,000 ft reels — all made in the USA and shipped same-day from fulfillment centers in LaPorte (TX), Miami Lakes (FL), and Rancho Dominguez (CA). Free shipping on orders over $10,000.
For deeper technical guidance, read our blog post: UL 4703 PV Wire: Why It Matters and How to Choose the Right AWG.
Frequently Asked Questions
What is UL4703 PV wire?
UL4703 is the Underwriters Laboratories standard for photovoltaic wire used in solar installations. It certifies cable for direct UV exposure, -40 °C to 90 °C wet (up to 150 °C dry), 600 V to 2000 V dielectric strength, flame resistance, and 25+ years of outdoor service life. NEC 690.31 requires PV Wire certified to UL4703 for most modern ungrounded solar installations.
What's the difference between PV Wire and USE-2?
PV Wire (UL4703) is purpose-built for solar arrays — UV-resistant, dual-insulated, and rated for ungrounded systems. USE-2 is a utility service-entrance cable that does not meet UL4703 requirements and is not approved for most PV string wiring under current NEC interpretations.
What AWG is most common for residential solar strings?
10 AWG UL4703 is the most common choice for residential 60-cell and 72-cell module strings with 9–12 A Isc. It provides 40 A base ampacity at 90 °C, which derates comfortably for typical rooftop conditions with 4-conductor bundles. See our 10 AWG 2000V 500 ft reel for the most popular SKU.
Why does voltage drop matter if the cable meets ampacity?
Ampacity is a safety minimum — it prevents cable overheating. Voltage drop is an energy-efficiency concern. A cable that meets ampacity but loses 3% to voltage drop will cost the customer hundreds of kWh per year in lost production over the system's 25-year life. Industry best practice keeps DC-side voltage drop ≤ 2% (ideally 1%).
Should I use 600V or 2000V PV wire?
Use 2000V PV wire for any modern grid-tied or commercial solar installation. Most string inverters support up to 1000–1500 V DC, and 2000V cable provides safety margin and complies with utility interconnection requirements. 600V cable remains valid for small residential or off-grid systems where string Voc stays well below 600 V even at cold-temperature Voc per NEC 690.7. Browse our 2000V collection or 600V collection.
Does this calculator follow the latest NEC code?
Yes. The calculator implements NEC 2023 Article 690.8 conductor sizing methodology, including the 1.25 × 1.25 factors, NEC 310.15(B)(2)(a) temperature correction, NEC 310.15(B)(3)(a) bundling adjustment, and NEC 240.4(D) small conductor protection. Always verify with your AHJ as code adoption varies by state.
How do I verify a cable is really UL4703 certified?
Check the jacket marking for: manufacturer name, UL mark, "4703", "PV WIRE", AWG size, voltage rating, and "SUNLIGHT RESISTANT". Then verify the manufacturer's UL File Number (E-XXXXXX) on iq.ulprospector.com. All PhotovoltaicCable.com PV wire ships with the UL listing visible on the jacket.
Is this calculator a substitute for an engineer's stamp?
No. This tool provides engineering guidance per NEC 690.8 for design and pre-quote sizing. Final designs for permitted installations must be reviewed and stamped by a licensed electrical engineer and meet your AHJ requirements. PhotovoltaicCable.com is not responsible for installation decisions made solely based on this tool.
What if my project needs a custom run length or color?
We stock standard reels (500, 1,000, 2,500, 5,000 ft) in black and red. For custom cuts, special colors, or aluminum DC feeders, contact our engineering team — most custom orders ship within 1–2 business days.
Do you ship internationally or only inside the United States?
We primarily serve the US market with same-day shipping from Texas, Florida, and California fulfillment centers. International orders require a custom quote — please contact us with your destination and quantities.